<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        function login(username,password,callback){
         setTimeout(()=>{
            if(username ==='zs'&& password === '123'){
                // return '登陆成功'
                callback('登录成功')
            }else {
                // return '登陆失败'
                callback('登陆失败')
            }
         },100)
        }
        // let result = 
        login('zs','123',function(res){
            console.log(res);
        });
        //console.log(result);  //undefined login函数没有返回值
    </script>
</body>
</html>